Method and apparatus for reducing particulate generation caused by door or cover flexing on high vacuum equipment

ABSTRACT

An inner lid is attached to a vacuum chamber, covering an inner region of the vacuum chamber. An outer lid, also attached to the vacuum chamber, covers the inner lid, leaving a region between the inner lid and the outer lid. A gas conduit allows gas to flow between the inner region of the vacuum chamber and the region between the inner lid and the outer lid. A filter is placed in or immediately outside the gas conduit to prevent particles from entering the inner region of the vacuum chamber from the region between the inner lid and the outer lid. Since the pressure is the same on the top and bottom of the inner lid, the inner lid does not flex and thus does not rub against the vacuum chamber when the vacuum chamber is pumped down or vented up.

This is a continuation of U.S. application Ser. No. 07/568,394 filedAug. 16, 1990 now abandoned.

BACKGROUND

The present invention relates to the design of covers and doors for highvacuum equipment to reduce particulate generation which is caused byflexing.

High vacuum equipment, for example, vacuum chambers such as processingchambers and load lock chambers used in the processing of integratedcircuits, are frequently pumped down and vented up. Due to the constantchange in pressure, a door or a cover to a chamber may be caused toflex. Unless the door or cover is sufficiently stiff and bolted down,the flexing of the door or cover will result in the door or coverrubbing at the location where the door or cover touches the chamberwalls. Such rubbing generates particles which can enter the chamber ascontaminants. Particulates also may be generated, to a lesser degree, bythe inward flexing surface of the cover.

SUMMARY OF THE INVENTION

In accordance with the preferred embodiments of the present invention, amethod and apparatus are presented for covering an inner region of avacuum chamber. An inner lid, attached to the vacuum chamber, covers theinner region. An outer lid, also attached to the vacuum chamber, coversthe inner lid, leaving a region between the inner lid and the outer lid.A gas conduit allows gas to flow between the inner region of the vacuumchamber and the region between the inner lid and the outer lid. A filteris placed in or immediately outside the gas conduit to prevent particlesfrom entering the inner region of the vacuum chamber from the regionbetween the inner lid and the outer lid. Since the pressure is the sameon the top and bottom of the inner lid, the inner lid does not flex anddoes not rub against the vacuum chamber when the vacuum chamber ispumped down or vented up.

In an alternate embodiment of the preferred embodiment of the presentinvention, an inner lid, attached to the vacuum chamber, covers theinner region. An outer lid, also attached to the vacuum chamber, coversthe inner lid, leaving a region between the inner lid and the outer lid.A first gas conduit allows the inner region to be pumped down or ventedup. A second gas conduit allows the region between the inner lid and theouter lid to be pumped down or vented up. However, while being pumpeddown or vented up, the inner region of the vacuum chamber and the regionbetween the inner lid and the outer lid are kept at the same relativepressure. Since the pressure is the same on the top and bottom of theinner lid, the inner lid does not flex and does not rub against thevacuum chamber when the vacuum chamber is pumped down or vented up.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified cross-sectional view of a vacuum chamber with acover designed according to a preferred embodiment of the presentinvention.

FIG. 2 is a simplified cross-sectional view of a vacuum chamber with adoor designed according to an alternate preferred embodiment of thepresent invention.

FIG. 3 is a simplified cross-sectional view of a vacuum chamberaccording to an another alternate preferred embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 is shown a simplified cross-sectional view of a vacuum chamber11. During pump down, a vacuum is introduced into an inner region 10 ofvacuum chamber 11.

An inner cover 16 is secured to vacuum chamber 11, for example, byscrews including a screw 18 and a screw 19. A seal 17 prevents leakagearound inner cover 16. An outer cover 12 is secured to vacuum chamber11, for example, by screws including a screw 14 and a screw 15. A seal13 prevents leakage around outer cover 12.

A conduit 22 connects inner region 10 to a region 20 between inner cover16 and outer cover 12. Gas flowing through conduit 22 keeps region 20and inner region 10 at the same pressure. The volume of region 20 isminimized to limit the volume of gas that needs to be removed from innerregion 10 during pump down.

Since the pressure is the same on the top and bottom of inner cover 16,inner cover 16 does not flex and thus does not rub against chamber 11when chamber 11 is pumped down or vented up. A filter 21 preventsparticles, which may be generated by rubbing of outer cover 12 againstchamber 11 resulting from flexing of outer cover 12, from entering innerregion 10.

One of numerous alternate embodiments of the present invention isillustrated by the simplified cross-sectional view of a vacuum chambershown in FIG. 2.

In FIG. 2, an inner cover 36 is secured to vacuum chamber 31, forexample, by restraints including a spring 38 on a guide 43 and a spring39 on a guide 44. A seal 37 prevents leakage around inner cover 36. Anouter door 32 on a hinge 35 is secured to vacuum chamber 31, forexample, by screws including a screw 34. A seal 33 prevents leakagearound outer door 32. When outer door 32 is opened, guide 43 and guide44 capture inner cover 36, causing inner cover 36 to open with outerdoor 32.

In order to insure that outer door 32 seals tightly to vacuum chamber31, it is recommended that hinge 35 have some play, as illustrated byoblong shaped hole 45. This allows outer door 32 to fully seat againstvacuum chamber 31 when a vacuum is introduced into inner region 30.

A conduit 42 connects an inner region 30 to a region 40 between innercover 36 and outer door 32. Gas flowing through conduit 42 keeps region40 and inner region 30 at the same pressure. The volume of region 40 isminimized to limit the volume of gas that needs to be removed from innerregion 30 during pump down.

Since the pressure is the same on the top and bottom of inner cover 36,inner cover 36 does not flex and thus does not rub against chamber 31when chamber 31 is pumped down or vented up. A filter 41 preventsparticles, which may be generated by rubbing of outer door 32 againstchamber 31 resulting from flexing of outer door 32, from entering innerregion 30.

Another alternate embodiment of the present invention is shown in FIG.3. In FIG. 3, an inner cover 116 is secured to vacuum chamber 111, forexample, by screws including a screw 118 and a screw 119. A seal 117prevents leakage around inner cover 116. An outer cover 112 is securedto vacuum chamber 111, for example, by screws including a screw 114 anda screw 115. A seal 113 prevents leakage around outer cover 112.

A conduit 123 connected to a conduit 125 connects inner region 110 to avacuum pump 124 and to a nitrogen tank 126. A conduit 122 connected toconduit 125 connects a region 120 between inner cover 116 and outercover 112 to vacuum pump 124 and to nitrogen tank 126. Vacuum pump 124pumps down inner region 110 and region 120 so that region 120 and innerregion 110 are at the same relative pressure. During the pump downprocess and while inner region 110 and region 120 are pumped down, avalve 128 isolates nitrogen chamber 126 from conduit 125. The volume ofregion 120 is minimized to limit the volume of gas that needs to beremoved during pump down.

Since vacuum pump 124 keeps pressure on the top and bottom of innercover 116 at the same relative pressure, inner cover 116 does not flexand does not rub against chamber 111 when chamber 111 is pumped down.

When inner region 110 and region 120 are vented up, nitrogen is slowlyreleased into conduit 125 from nitrogen chamber 126. Region 120 andinner region 110 are vented up while remaining at the same relativepressure. During the vent up process a valve 127 isolates vacuum pump124 from conduit 125. During vent up, the pressure on the top and bottomof inner cover 116 is kept at the same relative pressure and inner cover116 does not flex and does not rub against chamber 111 when chamber 111is vented. During pump down and vent up the system should typicallymaintain the pressure differential across inner cover 116 below 200Millitorr.

I claim:
 1. A method for sealing a vacuum chamber opening to preventflexion of the cover for the opening during changes in pressure in saidchamber, which comprises:(a) sealing the opening with a first, innernon-perforated cover; (b) covering the first inner non-perforated coverwith a second, outer cover leaving a region between the inner and outercovers that communicates with the vacuum chamber, whereby the differencein pressure between the vacuum chamber and the space between the innerand outer covers is maintained within 200 millitorr or less afterevacuation of the chamber.
 2. A method according to claim 1, wherein thepressure between the vacuum chamber and the space between the inner andouter covers is about the same.
 3. A method according to claim 1 whereina filter is maintained between the chamber and the space between theinner and outer covers.
 4. A method according to claim 1 comprising thefurther step of evacuating said chamber.
 5. A method according to claim4 comprising the further step of venting said chamber.
 6. A methodaccording to claim 5 wherein said chamber is vented by adding an inertgas to said vacuum chamber.